Pass launch argument to control XACRO logic

#xacro   #tutorial   #launch  

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Table of Content

LAB

• Control xacro from outside with args
• Bind xacro args to launch args

xacro

• Simple xacro file with arg and if

<?xml version="1.0"?>
<robot name="" xmlns:xacro="http://www.ros.org/wiki/xacro">
    <xacro:arg name="with_gripper" default="true" />
    <xacro:if value="$(arg with_gripper)">
        <!--with gripper-->
    </xacro:if>
</robot>

launch

• using command
• using OpaqueFunction function to get LaunchContext for substitute

Command

command

import os
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.substitutions import LaunchConfiguration, Command
from launch.actions import DeclareLaunchArgument, LogInfo

PACKAGE = "basic_mobile_robot"
SDF = "arg.sdf.xacro"


def generate_launch_description():
    with_grip = LaunchConfiguration('with_gripper')

    pkg = get_package_share_directory(PACKAGE)
    robot_description_path = os.path.join(pkg, "demos", "xacros", SDF)
    robot_description = Command(['xacro ', \
        robot_description_path, " ", "with_gripper:=", with_grip])

    log = LogInfo(msg=robot_description)
    arg = DeclareLaunchArgument(
            'with_gripper',
            default_value='true',
            description='Use grip')

    return LaunchDescription([
        arg,
        log
    ])

---

OpaqueFunction

test_xacro.launch.py

import os

from ament_index_python import get_package_share_directory
from launch import LaunchDescription, LaunchContext
from launch.actions import DeclareLaunchArgument, OpaqueFunction
from launch.substitutions import LaunchConfiguration
import xacro

PACKAGE = "basic_mobile_robot"
SDF = "arg.sdf.xacro"

def generate_launch_description():
    pkg = get_package_share_directory(PACKAGE)
    robot_description_path = os.path.join(pkg, "demos", "xacros")
    robot_description_file = os.path.join(robot_description_path, SDF)
    robot_description_file_out = os.path.join(robot_description_path, "arg.sdf")

    with_gripper_arg = DeclareLaunchArgument(
        'with_gripper',
        default_value="true",
        description="use with_gripper"
    )

    def render_xacro(context: LaunchContext, grip_arg):
        grip_arg_str = context.perform_substitution(grip_arg)

        doc = xacro.parse(open(robot_description_file))
        xacro.process_doc(doc, mappings={"with_gripper": grip_arg_str})
        out = xacro.open_output(robot_description_file_out)
        out.write(doc.toprettyxml(indent='  '))

    func = OpaqueFunction(function=render_xacro, args=[LaunchConfiguration('with_gripper')])

    ld = LaunchDescription()
    ld.add_action(with_gripper_arg)
    ld.add_action(func)
    return ld

usage

ros2 launch basic_mobile_robot test_xacro.launch.py with_gripper:="true"